Studies of aerobic energy metabolism in mammalian tissues and in parasites will be continued, particularly on the role of non-heme iron. Studies have been initiated of the energy metabolism in human platelets. Biochemical investigations of metabolic pathways and the respiratory chain of Entamoeba histolytica will be continued. Collaborative investigations of aerobic metabolism of Staphylococcus aureus, and of the interrelation of heme biosynthesis and respiration in liver will be resumed. Methodology includes differential centrifugations for isolating subcellular organelles, spectrophotometric techniques for determining difference spectra, and low-temperature paramagnetic resonance spectroscopy.